The same Rashidun Caliphate that ended with Ali getting assassinated and his son abdicating after an assassination attempt? Replaced by the Umayyad caliphate that was then quickly succeeded by the second Muslim civil war? I wouldn’t characterize calphates borne of wars of conquest to be a symbol of unity rather than what they are, empires not dissimilar to the US empire you’re arguing against.

Admittedly the Rashidun Caliphates should’ve really gotten their stuff together when it came to succession, but these were all wars of succession, not wars of secession. The idea that the Muslim world was meant to be ruled by one Caliphate was an assumption nobody tried to challenge. That’s unity. I like to compare it with the Roman empire, and I think we can agree that the Roman empire was mostly united. Anyway that unity continued until the late Abbasid reign when the Abbasid Caliphate started disintegrating, and stayed like that for a while until it got conquered by the Ottomans who held things together until WWI. The track record isn’t perfect, but it’s pretty good.

I just don’t see the US putting as much weight on shaping the middle east over time as oil becomes less and less relevant,

It’s not just oil. I mean a lot of it is oil, but it’s not just oil. The Middle East is a generally resource-rich region with a shared cultural identity and tendency towards unity (pan-Arabism and pan-Islamism are very common ideologies among Middle-Eastern people).

So I ran into this some time ago and setting aside the idea of whether these divisions did cause conflict or not, I think it’s telling that only two of these don’t have any sort of large-scale international influence, with one of those being the Islamic one despite being among the top in terms of people, resources and land area.